The conventional processes for manufacturing aluminum from bauxite, such as the Bayer process, produce ample quantity of a solid by-product called the red mud, termed so because of the high iron content. Not only does the aluminum industry emit an estimated forty million metric tons of greenhouse gases worldwide each year, they also produce an estimated 3 to 4 metric tons of red mud waste per metric ton of aluminum produced. Due to the environmental issues, the disposal of this red mud, in such large quantities, is a significant problem faced by aluminum industries world-wide. More often this waste is disposed on land or in sea, where the cost of transportation incurred is huge and land disposal can cause contamination of soil and groundwater. Therefore, the development of an economical method which exploits the values of the red mud waste to obtain useful products is of importance.
This red mud contains, apart from oxides of iron, a sizable quantity of other metals like aluminum, titanium, calcium, sodium, and silicon, mainly present as oxides, along with traces of toxic metals. Various methods have been proposed in the past to recover these valuable metals from the red mud slurry. However, most of these methods involve high temperatures or high pressures, therefore high energy consumption. Also, acid digestion of red mud has been suggested in the past to separate its components; however, this method provides a low level purity at high cost. Other methods like “stacking and drying”, addition of dispersants, coal dust mixing, addition of additives, have been proposed in the past to enhance the red mud consistency/flowability. Some of these disclosures describing the methods for treatment of red mud waste have been listed in the prior art below. Also, titanoferrous ores such as Ilmenite are processed to separate titanium chloride (TiCl4) and titanium oxide (TiO2) through a series of process steps which give huge volumes of waste streams containing substantial amount of ferrous as iron oxide and iron salts of chlorides or sulfates. The prior art below also lists methods for extracting ferrous from such waste streams.
WO2010079369 discloses a process for total recovery of pure oxides of the elements present in red mud sludge, as well as their partial transformation into high-value added products. The process comprises: heating the red mud residue with water to a temperature between 50-90° C.; after cooling to room temperature adding conc. hydrochloric acid to obtain a resultant solid to liquid ratio between 1:5-1:25; digesting the resultant mixture to obtain a first product containing soluble chloride salts of iron, aluminum, calcium, and sodium, and a solid residue containing titanium and silicon oxides; evaporating the first product and adding diluted hydrochloric acid to obtain a second product containing an enriched solution of chloride salts of iron, aluminum, calcium, and sodium, and an enriched solid residue containing titanium and silicon oxides; primarily separating the enriched solid residue and subsequently separating the iron, aluminum, calcium, and sodium. Using this process, no remnants of the red mud sludge remain.
US20090311154 discloses a zero-waste process for extraction of alumina from different types of bauxite ores and red mud residues and titanium dioxide from Ilmenite. The process comprises: smelting the mixture in the presence of a reducing agent to produce a molten slag, adding an alkali to the molten slag, isolating the molten iron from the resultant mixture to obtain residual slag, and recovering metal oxides from the residual slag. The process recovers most of the metal values and generates only small quantities of siliceous residues at pH 4-5.
U.S. Pat. No. 6,447,738 discloses a process for the extraction of alumina, iron oxide, and titanium dioxide from bauxite ore and clays, and other ore bodies and feed stocks. The process comprises: sulfuric acid leaching of the feed stocks in pressure autoclaves at about 200° C.; reducing the ferric values with SO2 to ferrous sulfate; removing potassium by crystallizing any double salt values of aluminum alkali sulfate; removing the crystals with SO2 gas and hydrolyzing the double salt into a basic aluminum alkali precipitated sulfate salt which is subsequently dried and calcined at 950° C.
U.S. Pat. No. 5,043,077 discloses a method for treating Bayer process red mud slurries to facilitate their handling. The method comprises adding to the slurry an amount of a substance consisting essentially of material of the class consisting of humic acids and humates, in the form of lignite or leonardite, effective to reduce the viscosity of the slurry.
U.S. Pat. No. 3,776,717 discloses a process for the treatment of red mud obtained in the production of aluminum, particularly for the reduction of alkali metals in the red mud and recovery of iron and aluminum. The method comprises: contacting the red mud with humic acid and burnt lime, and recovering the iron content by reduction of the iron oxides.
The present invention discloses a method for extracting valuable metals including aluminum, titanium, and iron from ores such as aluminoferrous ores, e.g. bauxite and titanoferrous ores, e.g. ilmenite, and residues containing alumina and titania, e.g. red mud slurries. From the prior art it is observed that these processes require an acid treatment, the effluents generated during such processes must be, therefore, neutralized before disposal. Also, the known processes require high temperatures and high pressures, therefore, energy intensive. The present invention suggests a method to overcome the afore-mentioned drawbacks of the prior art.